Chain drive systems have several components of undesirable noise and a major source of roller chain drive noise is the sound generated as a roller leaves the chain span and collides with a sprocket during the meshing process. The resultant impact noise is repeated with a frequency generally equal to that of the frequency of the chain meshing with the sprocket. As is known in the art, resilient cushion rings effectively reduce the generated noise levels associated with chain-sprocket meshing.
FIG. 1 shows a roller chain 10 in meshing engagement with an exemplary known roller chain sprocket 15 comprising metallic body 15B including a cylindrical hub 16 from which a row of outwardly projecting teeth T extend circumferentially around the hub 16. The teeth T are separated from each other by tooth spaces TS, each of which comprises and is partially defined by a root surface RS that extends between and interconnects circumferentially successive teeth T. The hub 16 projects or extends axially outward on opposite sides of the row of teeth T, and the sprocket 15 further comprises first and second elastomeric cushion rings (CR) 30, comprising nitrile rubber or the like, respectively bonded to the outside diameter OD of the hub 16 on opposite first and second sides of the row of teeth T. The cushion rings 30 extend completely circumferentially around the hub 16 and comprise alternating compression pads 32 and axially extending transverse grooves G30.
As shown in FIG. 1 and more clearly in FIG. 2, a pad 32 is substantially positioned on a sprocket tooth centerline CT1 (generally CT) and the number of pads and grooves in a cushion ring 30 will each equal the number of teeth T on the sprocket. The respective lower edges LE of the link plates of the roller chain 10, i.e., the inner or “roller” link plates RLP and the outer or “pin” link plates PLP, make contact with—and compress—the pads 32 of cushion rings 30 during the meshing process. In FIGS. 2-3A, only one of the cushion rings 30 is visible, but it is noted that the cushion ring 30 located on the opposite side of the sprocket 15 is identically structured and arranged on the sprocket 15, with common structural features angularly aligned with the visible cushion ring 30.
Each compression pad 32 includes a free height FH defined as the maximum distance by which the compression pad 32 projects radially above a fixed reference location on the sprocket body, such as the hub outside diameter OD or alternatively the axis of rotation of the sprocket body. Also, the free height circumscribes the cushion ring 30 at its high point radially outward. The compression pad 32 pad height PH is defined as the distance measured between the planar surface 32S—and normal to the planar surface—to a fixed reference location associated with the sprocket body 15B, such as a line that is tangent to the outside diameter OD or a line that passes through the axis of rotation.
Referring still to FIG. 2, the sprocket 15 rotates in a clockwise (CW) direction and a single link row LR1 of the roller chain 10 is shown at several positions of meshing progression with the link plate RLP1 perimeter having a solid line at the meshing start position and phantom lines at the interim meshing positions and at the full meshing position as the link row LR1 rotates about the center of seated roller RLR1 in a counter-clockwise (CCW) direction toward its full meshing contact at which time both the leading roller RLR1 and trailing roller RLR2 of the meshing link row LR1 are fully seated in their respective tooth spaces TS1,TS2 (generally TS) and in contact with the root diameter at location RD. It should be noted that the terms “leading” and “trailing” are in reference to the direction of travel of the chain 10 and the direction of rotation of the sprocket 15, wherein a leading features is located downstream and a trailing feature is located upstream in terms of the chain travel direction and the sprocket rotational direction. Also, the term “roller” as used herein is intended to encompass both a rotatable structure and a non-rotatable structure (e.g., a bushing) that seats in the tooth space TS1,TS2. The link row LR1 starts its meshing rotation at the instant the leading roller RLR1 impacts the sprocket body 15B in the sprocket tooth space TS1 at its theoretical meshing contact point RD (actually line contact at RD) on the root surface and concludes its meshing rotation when the trailing roller RLR2 (shown in phantom) impacts the sprocket body 15B at its meshing contact point RD in the tooth space TS2. It should be noted that the roller RLR2 is the trailing roller for link row LR1 as well as the leading roller for the adjacent trailing or upstream or next-meshing link row LR2 as shown in FIG. 3.
The tooth spaces TS1,TS2 comprise respective centerlines represented by respective tooth space center reference lines CTS1,CTS2 (generally CTS) that originate at the center or axis of rotation of the sprocket 15 and that bisect the respective tooth spaces TS1,TS2. The force vector FCR is a measure of the reaction damping force associated with the compression of the elastomeric cushion ring pads 32 by the link plates and FCR acts collinear with tooth space centerline CTS2 at the meshing impact point RD for the roller RLR2.
With continuing reference to FIG. 2 and particular reference also to FIG. 3, the link plates RLP1 of the link row LR1 contact and compress the pads 32 of the cushion rings 30 during the meshing rotation and the pad compression CMPR serves to beneficially diminish or soften the intensity of the meshing impact of the roller RLR2. As disclosed in U.S. Pat. No. 6,179,741, the entire disclosure of which is hereby expressly incorporated by reference, the elastomeric cushion rings 30 include planar compression pads 32 separated by transverse axially extending grooves G30. The centerline CG30 of each groove G30 is collinear with the centerline of a tooth space CTS (CTS1 & CTS2 in FIG. 3) and each compression pad 32 is compressed only by the link plates RLP1 in the meshing link row such that the chain link plates PLP2 of the next-meshing link row LR2 do not compress the pad 32 that is located between the first and second tooth spaces TS1,TS2 in which the leading and trailing rollers RLR1,RLR2 of the meshing link row LR1 are respectively received. The compression pads 32 have an inclined planar outer surface 32S and comprise a trailing corner radius 37 where the pad outer surface 32S transitions into a trailing groove G30. The planar surface 32S of each compression pad extends at an angle β from a trailing end of the pad outer surface 32S that is tangent to the trailing corner radius 37 to a leading end of the pad outer surface 32S that is tangent to a leading corner radius 38 where the leading end of the pad outer surface 32S transitions into the leading groove G30, where an angle β is measured relative to a reference line REF that lies parallel to the lower edge LE of the involved fully meshed chain link plate RLP,PLP that engages the compression pad 32 or a plane tangent to the link plate lower edge LE at its midpoint if the lower edge is not a straight line (alternatively the reference line REF can be said to be parallel to the pitch chord of the sprocket for the tooth spaces TS1,TS2 involved with the meshing link row LR1). The incline of the outer surface 32S of each compression pad 32 can alternatively be measured relative to the radial reference line CT1,CT2 (generally CT) passing through the tooth center of the tooth T that lies adjacent the compression pad 32. Thus, the outer surface of each compression pad 32 contacted by the chain link plates RLP,PLP is inclined such that minimum compression will occur in the proximity of the seated and pivoting leading roller RLR1, and maximum pad compression will beneficially occur in the proximity of the trailing meshing roller RLR2, where the compression CMPR will provide a greater resistance to meshing impact. The grooves G30 provide for minimum or no compression at the seated and pivoting roller RLR1, where compression would provide little or no benefit. Further, the grooves G30 provide voids or spaces for the elastomeric material forming the more highly-compressed trailing ends of the pads to move into during meshing and subsequent rotation through the sprocket wrap.
Referring also to FIG. 3A, the transverse groove G30 is formed by a first or leading groove radius 40 that has its arc center located on the tooth space centerline CTS2 and that is tangent to the second or trailing corner radius 37 of the leading or downstream pad 32 at its leading end and that is tangent to a second or trailing groove radius 42 at its trailing end. The trailing groove radius 42 also has its arc center located on the tooth space centerline CTS2 and is tangent at its outer end or trailing end to the leading corner radius 38 of the trailing or upstream pad 32. The groove G30 thus has a groove center CG30 that is aligned or coincident with the tooth space centerline CTS2.
FIGS. 3B and 3C show plan views of the compression footprint of the link plates RLP,PLP at their respective full meshing engagement positions. FIG. 3B corresponds to the sprocket position of FIG. 3 and shows the roller link plate compression footprint RL1C30 corresponding to the link row LR1. FIG. 3C shows the sprocket rotated one tooth angle to the point where the next link row LR2 is fully meshed with the sprocket 15 and shows the (thinner) pin link plate compression footprint PL230 for the link row LR2. In both cases, as noted above, it can be seen that only the chain link plates of the meshing link row compress the involved pad 32 that is located between the tooth spaces in which the leading and trailing rollers of the meshing link row are respectively received, i.e., the chain link plates of the upstream, next-meshing link row do not contact the compression pad 32 that is located between the tooth spaces in which the leading and trailing rollers of the meshing link row are respectively received. In other words, each compression pad 32 is only contacted by the link plates RLP or PLP of the meshing link row, and the compression pad is not contacted by the link plates PLP or RLP of the next-meshing or upstream link row.
The effectiveness of a resilient cushion ring is measured by its ability to adequately dampen the impact of a meshing roller. For a given design configuration, greater damping is achieved by increasing the deformation (i.e., compression) of the resilient cushion rings at meshing engagement. However, increased deformation could have an adverse effect on elastomer durability and compression set due to the resulting higher compressive stresses with the increased compression. It is therefore desirable to provide an improved cushion ring design configuration with enhanced durability and with equal or a greater level of damping at a reduced level of cushion ring compression.
Although the cushion ring sprocket 15 described above has been deemed highly effective and has found commercial success, a need has been identified for a new and improved cushion ring sprocket that provides improved durability and noise attenuation characteristics for reduced noise, vibration, and harshness (NVH) levels.